With a stiff upper lip and a tighter lid on the campaign treasury, Sen. Edward M. Kennedy (D-Mass.) said yesterday that he will continue his pursuit of the presidency but will focus it almost entirely on New England for the next few months.

Kennedy responded to his big loss in the Iowa caucuses Monday by shifting his travel schedule to allow more time in Maine and New Hampshire, the next two battlefronts of the 1980 campaign.

When a reporter asked Kennedy yesterday if he now must win the Feb. 11 Maine caucuses and the Feb. 26 New Hampshire primary, his answer, in its entirety, was, "Yes."

Kennedy's campaign staff, anticipateing a drop in contributions, moved to institute a new wave of austerity in what had been a high-spending campaign. "Instead of lobster dinner on the chartered plane, this operation will be peanut butter and jelly on the bus," said Tom Southwick, Kennedy's press secretary.

Southwick was referring to the decision to give up Kennedy's chartered Boeing 727 and rely instead on commerical flights from Washington to Boston and buses or small planes in New England.

The candidate's traveling staff also will be reduced campaign aides said. Instead of taking a crew of ghost-writers, typists and miscellaneous assistants on each trip, Kennedy now will rely on volunteers and workers at campaign offices in Manchester, N. H., and Portland, Maine.

Whether any other important changes will be made has not been decided. But Kennedy said yesterday that the basic message of his candicacy -- his claim that Carter has failed as a leader -- will not change.

Kennedy took the first loss of his 18-year political career with good spirit. Monday night at his headquarters here he was smiling and almost jaunty as he conceded to Carter. Yesterday he gave a polished, lively campaign speech to a convention of the machinists' union.

To deal with immediate money problems, the Kennedy staff plans a mailing to 15,000 nationwide who previously had contributed, but not the maximum allowed.

Some campaign aides were concerned that political endorsements might dry up in the wake of Kennedy's Iowa loss. He had number of endorsements from political and union officials in the works until Monday, but there was a fear at Kennedy headquarters that some potential endorsers might have second thoughts.